Process control method and apparatus

Abstract

A method and apparatus is provided for controlling the operation of a reforming furnace used to decompose at least a portion of a feed stream. A by-product fuel from subsequent process steps, which is a result of decomposition of the feed in the furnace, is used as one fuel source to fire the furnace. The control system monitors the byproduct fuel stream and the feed stream to a decomposition side of the furnace and determines the feed rate of additional fuel required to fire the furnace, which feed rate is correspondingly controlled. The control system includes means for determining various selected variables as sensed by suitable analyzers and flow rate meters and comparing certain variables to determine the flow rate of the additional fuel required to fire the furnace.

What is claimed and desired to be secured by Letters Patent is: 
     
       1. An apparatus which includes a control system, for controlling the addition of a first fuel to a using means, said apparatus including: first computing means operably associated with a feed stream containing a reformable hydrocarbon portion and operable for generating a signal AB representative of the volume flow rate of the feed stream reformable hydrocarbon portion to a first using means;   first means operable for providing a signal C representative of the combustion heating value per unit volume of a first fuel stream operable for supplying at least a portion of total fuel to the first using means;   second computing means operable for receiving the signal AB and generating a signal D representative of the required input of heat per unit time to the first using means;   third computing means operably associated with a second fuel stream and operable for generating a signal EF representative of the combustion heating value per unit time of the fuel comprising the second fuel stream, said second fuel stream being operable for supplying at least a portion of the total fuel to said first using means;   fourth computing means operable for receiving the signals D and EF and determining the difference between the signals D and EF to provide a signal G representative of additional heat per unit time required by the first using means;   fifth computing means operable for receiving the signals C and G and providing a signal H representative of the volume per unit time of the first fuel required by the first using means;   first control means operable for receiving the signal H and controlling the flow rate of the first fuel to the first using means in response to the signal H.   
     
     
       2. An apparatus set forth in claim 1 wherein: said first using means includes a furnace operable for cracking at least a portion of the feed stream by heating to a suitable cracking temperature with heat supplied to the furnace by combustion of the first and second fuels.   
     
     
       3. An apparatus as set forth in claim 2 wherein said first computing means including: a first multiplying computer;   a first flow rate sensing and transmitting means operably associated with the first multiplying computer and the feed stream and being operable for generating the signal A representative of the volume per unit time of feed flowing in the feed stream to a cracking side of the furnace and being further operable for transmitting the signal A to the first product computer; and   said first means including a first analyzing means operably associated with the fifth computing means, the first multiplying computer and the feed stream, said first fuel stream including a portion of the feed stream, and being operable for generating a signal B representative of the reformable hydrocarbon portion of the feed stream flowing into the cracking side of the furnace, and also operable for generating the signal C and being operable for transmitting the signal B to the first multiplying computer which is operable to multiply the signals A and B to produce the signal AB, said first analyzing means also being operable for transmitting the signal C to the fifth computing means.   
     
     
       4. An apparatus as set forth in claim 3 wherein said third computing means including: a second multiplying computer;   a second flow rate sensing and transmitting means operably associated with the second multiplying computer and the second fuel stream and operable for generating a signal E representative of the volume per unit time of the fuel flowing in the second fuel stream to a heating side of the furnace and being further operable for transmitting the signal E to the second multiplying computer; and   a second analyzing means operably associated with the second multiplying computer and the second fuel stream and being operable for generating a signal F representative of heating value per unit volume of the fuel and being further operable for transmitting the signal F to the second multiplying computer which is operable to multiply the signals E and F to produce the signal EF.   
     
     
       5. An apparatus as set forth in claim 4 including: a first conduit means operable for flow of the feed stream therethrough from a source of feed to the cracking side of the furnace; and   a second conduit means communicating with the first conduit means upstream of the first flow sensing means and also communicating with the heating side of the furnace and operable for supplying a portion of the feed stream to the heating side of the furnace as at least a portion of the first fuel.   
     
     
       6. An apparatus as set forth in claim 5 wherein: said first using means is an ammonia synthesis apparatus and said second fuel stream is a by-product from a portion of the ammonia synthesis apparatus.   
     
     
       7. A method for controlling thermal cracking of at least a portion of a feed hydrocarbon stream wherein heat is supplied for cracking by the combustion of a fuel stream and a supplemental fuel stream, said method including the steps of: measuring the cracking heat input per unit time requirement for a predetermined level of cracking of said portion of the feed hydrocarbon stream;   measuring the combustion heating value per unit time of the fuel stream;   determining the quantity per unit time of supplemental fuel needed to supplement the combustion heating value of said fuel stream to produce the required cracking heat input; and   combining the required amount of the supplemental fuel with fuel from said fuel stream.   
     
     
       8. A method as set forth in claim 7 including measuring the combustion heating value per unit time of the supplemental fuel stream. 
     
     
       9. A method as set forth in claim 8 wherein: at least a portion of products resulting from the cracking are used for synthesis of ammonia; and   said fuel is a by-product fuel from the ammonia synthesis process.   
     
     
       10. A method for controlling thermal cracking of at least a portion of a feed hydrocarbon stream wherein heat is supplied for cracking by the combustion of a fuel stream and a supplemental fuel stream, said method including the steps of: producing a signal D representative of the heat input per unit time required for a predetermined level of cracking of said portion of the feed hydrocarbon stream;   analyzing said fuel stream and producing a signal F representative of the heating value of the fuel of the fuel stream;   measuring the flow rate of said fuel stream and producing a signal E representative of the flow rate;   multiplying the signals E and F and producing a signal EF representative of the heating value per unit time of the fuel of said fuel stream used in combustion;   subtracting the signal EF from the signal D and producing a signal G representative of additional heat required for cracking; and   adding supplemental fuel for combustion in response to said signal G.   
     
     
       11. A method as set forth in claim 7 wherein said supplemental fuel is a first portion of said feed hydrocarbon stream; and further including: analyzing said feed hydrocarbon and producing a signal C representative of the heating value of said feed hydrocarbon;   dividing the signal G by the signal C and producing a signal H representative of the volume per unit time of feed hydrocarbon needed as supplemental fuel;   controlling the flow rate of added supplemental fuel in response to the signal H.   
     
     
       12. A method as set forth in claim 11 including: measuring the flow rate of a second portion of feed hydrocarbon to be cracked and producing a signal A representative of the flow rate of the second portion;   producing a signal B representative of the concentration of reformable hydrocarbon in the feed hydrocarbon;   multiplying the signals A and B and producing a signal AB representative of the volume per unit time of the reformable hydrocarbon to be cracked;   multiplying the signal AB by a set point to produce the signal D.